Chromosomes show regular orders of compaction of the long DNA backbone. This compaction varies with stages in the cell cycle and with active or inactive status of chromosome segments. The organization of the 100A fiber as closely packed string of histone beads is becoming clear and its coiling into the 200 A fiber has been documented. My emphasis will now be on clarifying the higher order of compaction, namely interphase chromomeres (using polytene chromosomes) mitotic and meiotic chromonema and chromomeres and metaphase chromosome structure. The high voltage electron microscope will be the major tool here. Histones 1 seem to play a major role in these higher orders. The differential behavior of heterochromatin and Giemsa bands to extraction of H1 suggests that subfractions modified histones might be involved. This hypothesis will be further tested. In collaboration with Patricia Witt the structural and functional organization of the kintochore in mammalian chromosomes will be further investigated. BIBLIOGRAPHIC REFERENCES: 1976 Ris, H. Chromosome Structure, in Developmental Genetics ed. Fenoglio, Goodman and King, Stratton Intercontinental Medical Book Corp., New York. 1976 Ris, H. Levels of chromosome organization. Sixth European Congress on Electron Microscopy, Jerusalem pp. 21-25.